Spark plug



June 24, 1930. H. RABEZZANA 1,768,330

S PARK PLUG Filed Dec. '7, 1928 Patented June 7 24, 1930 UNITED STATESPATENT OFFICE HRUIOB RABEZZANA, OF FLINT, MICHIGAN, ASSIGNOR TO A CSPARK PLUG COMPANY, OF FLINT, MICHIGA N, A COMPANY OF MICHIGAN SPARKPLUG Application filed December 7, 1928. Serial No. 324,509.

It is a general object of this invention to contribute to theetficiency, reliability, and durability of spark plugs; and this inven-.tion relates, so far as its immediate commercial use is concerned,exclusively to .the inte rior insulation of spark plugs comprising micawashers, or the like.

It being Well known that internal combustion engines are liable tofunction unsat- 10 isfactorily when spark plugs and/or adjacent partsare unduly cold and also when said parts are excessively hot, and wellknown also that leakage and rapid deterioration may result from markedinequalities of temperature in the parts of spark plugs, it is an objectof this invention to provide spark plug constructions which tend towarda prompt equalization of temperature throughout mica insulation, or thelike, by

a limited conductionof heat away from exposed surfaces thereof; andpreferred embodiments of this invention also tend at all times toprevent such local overheating of spark plug parts as to involve dangerof preignition or other detrimental effects.

' Various features of the spark plugs disclosed being elsewheredescribed and claimed, the present application is directed moreparticularly, as indicated by the above title, to 20 a novel use ofso-called sandwich insulation, this being produced by interposition ofheat conductor elements between insulating elements and employed inassemblies disposed in the region of the spark gaps of the plugsreferred to. The special type of insulation herein referred to mayappear paradoxical, in that the sheets or washers of highly conductivemetal, such as copper, are interposed between sheets or washers of aninsulating material such as mica; but it should be understood that it isa vprimary object of this invention favorably to modify the headgradient within insulated assemblies of the general character referredto.

The edges of mica washers secured in proximity to s ark gaps beingunavoidably exposed to hig temperature and high pressures, and the lowthermal conductivity of such washers having been found to tend towardleakage and avoidable deterioration,

this invention aims at what might be termed a compromise in regard tothe local overheating problem,by so proportioning and using interposedmetallic washers as to obtain, while avoiding unduly close proximitybetween oppositely charged metallic parts, a satisfactory flow of heatinto and through such insulating washers. This is preferably done insuch manner as to assure a satisfactory balance of tendencies, bothduring starting and during continued operation and advantageousembodiments of this invention may comprise assemblies of the mentionedsandwich type insulation in connection with either an inner electrode ora grounded electrode shell, or in connection with both.

Other objects of this invention including various optional oralternative features of construction, may be best appreciated from thefollowing descriptions of embodiments thereof, taken in connection withthe appended claims and the accompanying drawings.

Figure 1 is a vertical or longitudinal sectional view through one simpleand advantageous form of spark plug illustrating the present invention.

Figure 2 is a somewhat similar view, with some arts shown in elevationand some parts roken away, showing an alternative form.

Figure 3 is a view, corresponding to the lower portion of Figure 2 butshowing an additional alternative form.

Reserving for final description that simple and advantageous form shownin Figure 1,

attention may be first directed to those intev rior parts shown inFigure 2 as disposed form of a special bushing 15, but also with aninterior insulation assembly 16,-the latter being of that sandwich typeupon which protection is herein sought.

The bushing 15 being illustrated as of the so-called rough-neck type, amica sleeve or cigarette 17 and a protecting tube 18 are shown asdisposed concentrically upon the electrode 11 and within said bushing insuch manner that the inward collapse of weakened zones 19, 20 and 21, aseffected by a deformation of said tube, serves not only to retain thebushing 15 in such a position upon the electrode 11 as to hold the innerinsulation assembly 16 under a desired compression, but also to obviateleak- -age longitudinally of said electrode. Either the mentionedbushing and/or the shell 10 may be of any desired alternative type, sofar as concerns the present invention; and. a gasket 22 being suitablyinserted, the shell 10 is shown as having been also exposed to athermoplastic collapse in an intermediate zone 23,-presumably after orin addition to an inward deformation of a retaining flange 24, adaptedto engage a rounded sur face 25, provided by the bushing 15.

In the form shown in Figure 2, s0-called sandwich insulation beingtherein employed only in connection with the interior insulationassembly 16, separate sheaves 26, 27, 28, 29 and 30 of mica insulationare shown as separated by metallic washers 31, 32, 33 and 34,-the washer34, if employed at all, being optionally of such interior diameter as tospace the same from the electrode 11 and being optionally provided witha leak-preventing annular extension contacting with and/or gripped bythe insulation sleeve 30. If desired, the washer 34 may be formedintegral with the metallic element of a copper-asbestos gasket 22; or itmay be otherwise adapted to serve as a wedge-fitting and leak-preventingelement contacting with a suitable surface provided within the lower orinner section 10" of the shell 10 or its equivalent; but it will beunderstood that, as illustrated in the case of the metallic washers3132, the conductive elements carried by any inner electrode elementwill ordinarily be of such interior diameter or diameters as to insureheat-conductive contact therewith; and an entire electrode spindle,comprising all the elements shown and mentioned as carried by theelectrode 11, may ordinarily be assembled and thereafter seated underpressure within any shell 10, in advance of the inward deformation ofthe flange 24 and by such a thermoplastic collapse of the weakened zone23 as to assure a subsequent contraction of said shell and the retentionof all parts in their indicated relationships.

.In Figure 3, a shell 10 is shown as rece ving an electrode 11 which isprovided with a head 12, a bushing 15 being so inwardly collapsed asradially to compress a cigato retain under a desired compression aninner insulation assembly 16 and the bushing 15 and shell 10 are shownas respectively provided with oppositely facing shoul- I ders 35 and 36adapted to cooperate in the retention of an auxiliary insulationassembly 37.

Either or both of the insulation assemblies shown in Figure 3 may be ofthe sandwich type. The assembly 16 is shown as including, in addition tointerposed metallic washers 32 and 33 corresponding in both interior andexterior diameter with the adjacent mica washers, a special washer 31,interiorly provided with a conductive flange which engages the electrode11, and also with special washers 34 and 38 whose interior diameter soexceeds the diameter of the electrode 11 as to obviate risk ofelectrical conduction thereto; and the washer 38 is shown as providedwith an exterior flange so interposed between the upper portions of theinsulation assemblies 16 and 37 as to assure a wedging andleak-preventing effect. In the case of the auxiliary insulation assembly37 adapted not only to be radially wedged but to be held under axialcompression in substantially the same manner as the gasket 22 of Figure2, metallic washers 39, 40 and 41 are shown as corresponding in allhorizontal dimensions with the adjacent mica washers; but, merely by wayof further illustrating possible special constructions that fall withinthe scope of the present invention, the washers 42 and 43 are shown notonly as of greater interior diameter than the adjacent washers (thisconstruction tending to obviate risk of an unintended sparking betweenwashers employed in the insulation assembly 16 and the washers 42?, 43),but also with an interconnecting web of flange 44,-deemed especiallyeflective, like the flange provided upon the washer 31, in assuring adesired conduction of heat from said washers to the adjacent electrode.

In that simple and advantageous embodiment shown in Figure 1, anelectrode 11", provided with a stop in the form of a shouldered head.12", is shown as having collapsed thereon both a stop element in theform of a nut 13, of so-called air craft type, and also an intermediateretaining element or stop in the form of a bushing 15", an innerinsulation assembly 16 being interposed between thehead 12 and thebushing 15 and an outer insulation assembly 14* being interposed betweensaid bushing and the nut 13, to complete a pro-formed inner electrodespindle secured within a shell 10". Said shell is shown as providing ashoulder or seat 36 adapted to coo )erate with an opposing face 35",provided y a sheaf of mica insulation 26", included within the innerinsulation assembly 16*, in the retention of an auxiliary insulationassembly 37"; and the latter may consist exclusively of mica sheaves 45interposed between metallic washers 39*, equal thereto in both interiorand exterior diameter. In this embodiment of the present invention itwill be understood that, all parts between the head 12* and the nut 13being preassembled under a suitable axial pressure (as by athermoplastic collapse of the nut 13", substantially as indicated at46*), the auxiliary insulation assembly 37 may be put and kept under adesired axial compression incidentally to an inward deformation of theflange 34", or its equivalent (a gasket being shown as interposed at 22between shoulders 47 and 48 provided respectively on the shell 10 andthe bushing 15), and/or by a thermoplastic collapse of a reduced or'otherwise weakened zone 23 of the shell 10", or its equivalent.

It will be appreciated that the comparatively simple construction lastdescribed involves the use of but one type of conductive washer; thatthe steps involved in its assembly are comparatively few andinexpenpresent invention as the latter are indicated in the followingclaims.

I claim: 1. Aspark plug com rising: an inner elec trode element, provied with a head; a grounded electrode shell element surrounding saidinner electrode element and'sandwich type insulation, comprisingthermally conductive elements interposed between electricallynon-conductive elements and so disposed between said electrode elementsin the region of said head as to augment the flow of heat from saidregion.

2. A spark plug as defined in claim 1 in which sandwich type insulationis carried by type insulation being comprised in an auxiliary insulationassembly.

. 5. A spark plug as defined in claim 1 in which said inner electrodeelement is comprised in a spindle, some of said sandwich type insuIationbeing comprised in an auxiliary insulation assembly which is held undercompression through said spindle.

6. A spark plug as defined in claim 1 in which some of said thermallyconductive elements are metallic washers interposed, be-' tween micawashers and in heat-conductive contact with one of said electrodeelements.

7 .A spark plug as defined in claim 1 in which some of said thermallyconductive elements are metallic washers interposed between mica washersand substantially equal thereto in both interior diameter and exteriordiameter and in heat-conductive contact with one of said electrodeelements.

8. A spark plug as defined in claim 1 in which some of said thermallyconductive elements are opposite said head and so differ from adjacentnon-conductive elements in diameter as to obviate sparking thereto.

9. A spark plug as defined in claim 1 in which some of said thermallyconductive .ele-

ments are immediately above said head and so contact with said innerelectrode as to facilitate thermal conductiontherethrough.

10. A spark plug as defined in claim 1 in which some of said thermallyconductive elements so contact with said shell as to facilitate thermalconduction therethrough from said region.

11. A spark plug as defined in claim 1 in which some of said thermallyconductive elements are provided with conductive flanges engaging anadjacent electrode element.

12. A spark plug as defined in claim 1 in which some of said thermallyconductive elements are interconnected by thermally conductive webs.

13. For use in a spark plug, sandwichtype insulation comprising:thermally conductive elements interposed between electricallynonconductive elements, some of said thermall conductive elements beingwashers 'whic differ in diameter from said electrically non-.

conductive elements in such manner as to facilitate thermal conductiontherethrough and nevertheless to obviate electrical conductiontherethrough.

In testimony whereof I afiix my signature.

HECTOR RABEZZANA.

said inner electrode element and immediately above said head.

3. A spark plug as defined in claim 1 in which sandwich type insulationis carried opposite said head and by said shell element.

4. A spark plug as defined in claim 1 in which said inner electrodeelement is comprised in a spindle, some of said sandwich

